Laser light poses several safety risks to humans, based on the coherent nature of laser radiation. The potential for eye damage is often the modality that requires the most stringent limits on laser power. In controlled environments (e.g. a laboratory) precautions can be used such as protective eyewear or housing a laser in a specialized enclosure with safety interlocks. In open environments (e.g. streets and highways) such precautions cannot be assumed and hence eye-safety is often ensured by using inherently eye-safe lasers (e.g. ANSI Z136.4 class 1 lasers).
Laser range finding is a useful technology for autonomous vehicles but must operate safely in human-filled environments. Maximum measurement range can benefit from higher laser intensity. However, many countries and regions of the world impose varying limits on the maximum permissible laser radiation (e.g. energy per square centimeter or energy per pulse). Traditionally, adherence to these laser radiation limits is ensured by design and validated during the laser system qualification. This designed-in approach to limiting laser radiation exposure is conservative and often suboptimal. Recent, alternative approaches attempt to sense objects in the vicinity of a laser that is operating above an intrinsically safe (e.g. eye-safe) threshold. The intensity of a laser beam can decrease as it travels from a source and hence it may only be necessary to monitor for objects (e.g. people) within a threshold distance from the source to ensure safe laser operation. U.S. Pat. No. 9,121,703 issued to Droz discloses using a proximity sensor to sense an object within a threshold distance of the laser range finder and discontinuing laser emission upon detection. Proximity sensors (e.g. passive infrared sensors) are useful for identifying objects in the vicinity but provide little specificity regarding location and the path or trajectory of objects in the field of view (FOV) of the laser system. Proximity-based laser-deactivation can be useful when a laser system emits high-intensity laser light in a wide range of azimuthal directions (e.g. 360 degrees) but can be overly-conservative (e.g. produce many false positives) for a laser system that emits high-intensity pulses in only a narrow range of directions.
U.S. Pat. No. 8,948,591 to Scherbarth discloses a laser range finder that detects objects within a threshold distance during some previous time period and discontinues laser emission upon detecting an object within the threshold distance. This approach does not address the challenge of high-intensity laser pulses during the discovery of a new object within the threshold distance. Several safety standards (e.g. ANSI Z136.4) require all laser pulses meet an eye-safe intensity requirement, even a single laser pulse during discovery of a new object.
Therefore, an ongoing technical challenge is the operation of a laser range finder in a high-intensity mode while ensuring safety and avoiding frequent false positive laser power reductions.